1. Field of the Invention
The invention relates to a liquid container that supplies liquids such as ink to a liquid using unit of a recording unit such as a pen and a print head; a liquid supply system that is the combination of such a liquid container and liquid using unit; and a liquid using apparatus employing such a liquid supply system, an ink tank, an ink supply system, inkjet print head and a print apparatus employing such an ink supply system.
2. Description of the Related Art
Some of the liquid using apparatuses, such as an inkjet print apparatus that forms images on a printing medium by applying a liquid ink thereon using an inkjet print head, form images on a printing medium by moving a print head thereover and ejecting ink thereto. Others may form images by moving, in turn, a printing medium over a fixed print head that ejects ink thereto.
One of the methods for supplying ink to the print head of such an inkjet print apparatus is called the on-carriage method in which an ink tank installed, inseparably or separably, in the print head that is mounted on a carriage and the like and shuttles (scans) supplies ink. Meanwhile, there is another-method called the tube method in which an ink tank, separate from the print head mounted on the carriage, is fixed on another unit of the print apparatus and the ink is supplied from the ink tank to the print head via a flexible tube. In the methods, there is included such a method. In which a second ink tank serving as an intermediate tank between the ink tank and the print head is mounted on the print head or the carriage.
In the prior art of the ink tank from which the ink is supplied directly to the print head, there is the one that has a deformable, flexible, sealed, bag-shaped member which holds ink and a spring member which generates a negative pressure in the bag-shaped member by applying a force to expand the deformable portion. This negative pressure lies in a pressure range for the print head to enable to eject ink in equilibrium with ability for holding meniscus formed at an ink ejection port of the print head.
In such an ink tank of this mechanism, however, the force exerted by the spring increases as the ink decreases during ink consumption. Then the negative pressure inside the bag-shaped member grows and eventually exceeds the negative pressure limit below which the print head can eject ink. As a result, a problem arises that the ink tank becomes useless before all the ink in it has been consumed.
There are ink tanks of another type that hold ink in a bag-shaped member of which a material and shape is properly selected so that the bag-shaped member itself generates a negative pressure. Although such an ink tank becomes flat leaving no space in it when ink has been completely consumed, there is a limit to the shape of such a bag-shaped member. Thus when one tries to fit such an ink tank in the housing, the bag-shaped member filled with ink does not fit well in the housing, leaving dead space in the ink tank. In addition, since the negative pressure grows also in such a bag-shaped member as the ink is running out, there arise problems that the ability to supply ink to the print head may decrease and ejecting operation of the print head may become unstable.
Meanwhile, Japanese Patent Application Laid-Open Nos. 7-125240 (1995) and 7-125241 (1995) disclose an ink tank that has a mechanism to introduce air into the flexible container as the internal negative pressure grows, so that the negative pressure can be kept in the proper range. It is proposed that a generally tubular orifice made of a ball and a boss is formed. In this structure, a tubular boss leading from the outside into the container is formed and the ball of which outer diameter is smaller than the inner diameter of the boss is located in a plurality of projecting ribs formed in the inner wall of the boss. Such an orifice has a size such that a small amount of ink serves as a liquid seal due to capillary action of the ink. And its shape is selected so that the negative pressure inside the container overcomes the capillary action of ink and the liquid seal of the ink becomes inactive as the negative pressure approaches the limit level of the print head for normal operation. Specifically, the container introduces air thereinto to decrease the negative pressure, so that the print head may continue normal operation.
The above structure provides a sealed system held by the balance between the ability for holding meniscus formed at a tubular orifice (a liquid seal) and the negative pressure applied by the spring. Although the mechanism itself is relatively simple, the structure has the following problems. Namely, because of pressure difference between the outside and the inside of the container, decrease in the ink viscosity due to increased temperatures, shock and fall of the ink tank during handling, particularly in the serial printing, acceleration applied during scanning and other factors, the liquid seal is broken and the ink leaks out. In addition, since the liquid seal is rather affected by humidity changes including drying up, air may not be smoothly introduced into the tank. Then the ink supply ability to the print head is affected and printing quality deteriorates accordingly.
To avoid such problems, the above Patent Application Laid-Open Publications disclose a structure in which an inlet maze that works as an overflow container is communicated with the boss and thereby ensures the humidity gradient. However, the structure becomes complex.
There is another concern that air rushes into the container when the ink held in the container is running out. Then the ink left in the print head may leak out from the ejection port and the tubular orifice where the meniscus has not formed.
Furthermore, the dimensions of the boss and the ball, in other words, the size of the orifice, should be designed based on the physical properties of ink, such as ink viscosity, container size and other factors. Thus each time there is a change to such factors, the orifice design must be modified accordingly.
The present invention has been made to solve the above problems, and one of its aspects is to prevent liquid leakage regardless of the using conditions and the reserving atmosphere and stabilize the container negative pressure characteristic regardless of the degree of liquid consumption, by having a one-way valve in the liquid container (ink tank) that supplies liquids such as ink to an external device such as a print head, maintaining the negative pressure formed in the liquid supplying passage positioned in the downstream of a position where a fluid is supplied by the one-way valve.